Hydraulic control valve assembly

ABSTRACT

A valve assembly comprising a plurality of distributor valves for operation of a plurality of hydraulic motors is provided with a plurality of inlets for a plurality of supply sources. The distributors are interconnected so that the implements may be operated by separate sources or the sources combined for selective operation of certain implements.

United States Patent [1 1 Bianchetta et al.

[ 1 Sept. 18, 1973 HYDRAULIC CONTROL VALVE ASSEMBLY [75] Inventors: Donald L. Bianclletta, Coal City;

Kenneth R. Lohbauer, Joliet, both of 111.

[73] Assignee: Caterpillar Tractor Co., Peoria, 111.

[22] Filed: Dec. 13, 1971 [21] Appl. No.: 207,028

[52] U.S. Cl 137/596, 60/52 HE [51] Int. Cl. F151) 13/06, Fl6k 11/07, F15b 11/00 [58] Field of Search 137/596, 596.13,

[56] References Cited UNITED STATES PATENTS 3,543,644 12/1970 Stacey 60/52 HE 2,103,530 12/1937 Henry 60/52 HE X 3,350,986 11/1967 Berta et a1. 91/414 3,530,883 9/1970 Kramer 137/596 3,543,646 12/1970 lijima 60/52 HE Primary ExaminerHenry T. Klinksiek Assistant ExaminerRobert J. Miller Attorney-Freling E. Baker [57] ABSTRACT A valve assembly comprising a plurality of distributor valves for operation of a plurality of hydraulic motors is provided with a plurality of inlets for a plurality of supply sources. The distributors are interconnected so that the implements may be operated by separate sources or the sources combined for selective operation of certain implements.

9 Claims, 7 Drawing Figures PAIENIEB 8573 saw 1 or 5 lllqllql l I I DONALD L. BIANCHETTA KENNETH R. LOHBAUER I O I PATENTED 3.759.292

SHEU 5 BF 6 TIE-T E- INVENTORS DONALD L. BIANCHETTA KENNETH R. LOHBAUER ATTORNEYS PAIENTED 3.759.292

SHEET 6 0F .6

Z40 24 INVENTORS T L DONALD L. BIANCHETTA KENNETH R. LOHBAUER ATTORNEYS BACKGROUND OF THE INVENTION This invention relates to valves, and pertains, more particularly, to a plurality of cooperating distributor valves.

Backhoes and hydraulic excavators have come into widespread use because of their versatility. They can, for example, serve the function of loaders, ditchers, and small cranes.

One drawback of such machines, however, has been their inability to use the maximum power input to the machine at maximum efficiency. The hydraulic systems of such systems are known to employ a pair of pumps for supplying the circuits for operation of a plurality of motors. The motors normally have separate circuits so that two or three motors are supplied by one pump and two or three by the other. This insures that one motor supplied by each pump can be operated simultaneously. However, if the flow from one pump is not being used, then it goes to waste. Also, pumps are expensive, and each pump adds considerable cost to the price of the machine.

Some proposals have been made for combining the fluid from two pumps for operation of one or more motors, but such proposed systems have been unsatisfactory. Some such proposals require a complete diversion of fluid from one system to the other, with the result that one system is inoperative.

Prior art approaches to combining fluid from two pumps are shown in U.S. Pat. No. 2,767,550, issued Oct. 23, 1956 to R. Lapsley, and US. Pat. No. 2,322,740, issued June 22, 1943 to HR. Vanderzee et al.

Other proposals provide for a parallel connection of all motors downstream of the track drive motors. This results in a loss of positive operator control by the stalling of heavily loaded motors and overrunning of lightly loaded motors.

Still others have proposed a combining of the pumps after the track drive motors with the remaining motors series connected. This results in a system where no fluid is available to downstream motors when the first motor in the series is being operated. That is, the system can supply only the priority upstream demand.

SUMMARY OF THE INVENTION Accordingly, it is the primary object of the present invention to provide a control valve arrangement for a hydraulic system that overcomes the above disadvantages of the prior art.

Another object of the present invention is to provide a control valve assembly that is operative to maintain a plurality of fluid sources separate for separate operation of a plurality of fluid motors and to automatically combine the flow from the plurality of sources for actuation of selected motors.

A further object of the present invention is to provide a hydraulic control valve assembly for combining the output from multiple fluid pumps in order to supply one or more implements with the combined output from the multiple pumps.

Another object of the present invention is to provide a valve system having the operative advantages of a series connected system and the combining advantages of a parallel system.

A major advantage of the present system is that a plurality of sources can be used independently or can be selectively combined for use.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and advantages of the present invention will become more apparent from the following specification when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic layout of a control system for a hydraulic excavator incorporating the valve assembly of the present invention;

FIG. 2 is a schematic illustration in section, of an embodiment of the present invention;

FIG. 3 is a schematic illustration of a modified form of the present invention;

FIG. 4 is a sectional view of a valve assembly constructed in accordance with the present invention;

FIG. 5 is a section taken along lines V--V of FIG. 4;

FIG. 6 is a section taken along lines VIVI of the valve assembly of FIG. 4; and,

FIG. 7 is a schematic illustration of a further embodiment of the present invention.

DETAILED DESCRIPTlON OF PREFERRED EMBODIMENTS Referring now to the drawings and specifically to FIG. 1, there is illustrated a circuit for a hydraulic excavator which is self-propelled and in which all the operations are performed by hydraulic power. The power for the hydraulic system is supplied by two main identical variable displacement pumps 10 and 12, a smaller pump 14 and an auxiliary pump 16, all drawing fluid from a sump or tank 18, and driven by a suitable engine, not shown. The pump 14 may be fixed or variable displacement to suit the needs of the system. The main variable displacement pumps 10 and 12 are suitably connected together by means of a regulator 20 which is responsive to the needs of the system to regulate the pumps 10 and 12 to supply optimum pressure and/or flow as required by the system. As will be explained later, the regulator 20 and the unique valve assembly arrangement of the present system cooperate to provide a system having maximum efficiency. Ordinarily the two main pumps 10 and 12 will each supply one half of the working components of the excavator, however, in the interest of safety, the preferred embodiment provides for a separate platform swing circuit, as will be explained later. Furthermore, the valving system provides for combining of the fluid flow from pumps 10 and 12 for selected operation of certain components at a higher rate of movement.

The regulator or horsepower limiting means 20 allows the engine output to be distributed to the pumps according to the requirements of each pump. Although both pumps 10 and 12 may'deliver the same quantity of oil, the operating pressure of each will vary according to the function that the excavator is performing. Therefore, the available engine power can be unevenly distributed to the various machine elements in accordance with the power needed at the time.

The pump 10 supplies fluid by way of a conduit 22 to a bank of distributor valves comprising distributor spools or valve stems 24, 26 and 28 which are operatively connected to distribute fluid respectively to track drive motor 30, a bucket motor 32, and the boom motors 34. The pump 12 supplies fluid along the conduit 36 to a bank of valves comprising distributor valves 40 and 42 and cross-over valve 44, which are operative to distribute fluid to a track drive motor 48, and a dipper or stick motor 50.

Pump 14 supplies fluid to a distributor 38 for operation of a slew motor 46. This fluid, if not used, may either go to exhaust, as illustrated, or may be available for combining downstream with fluid from pump 12 for operation of other implements as will be hereinafter explained. The auxiliary pump 16 supplies fluid for pilot operation of the main control valves as well as for operating brakes for the track drive motors and the slew motors.

A schematic layout of a valve assembly is illustrated in FIG. 2 with all the passageways and elements revolved about an axis to the same plane to facilitate comprehension. The valve assembly comprises a housing 52 having a plurality of bores 54, 56, 58 and 60, in which are slidably mounted the control spools 38, 40, 42, and crossover spool 44. The axes of the spools are intersected by a common plane and the bores are intersected by a through passage 62 and two branches 64 and 66 of a low pressure exhaust passageway. A plurality of inlet passages comprising a first passage 68 for supplying fluid to the first spool 38, a second inlet passage 70 for supplying fluid to the spool 40 and a third inlet passage 72 are provided for supplying fluid to the control spools of the valve assembly. Each of the valve spools are double acting, which means they are operative to direct fluid to a double acting or reversible hydraulic motor. The inlets 68 and 70 can be supplied by separate fluid sources or supplied by a single source using flow dividing means. The three spools 38, 40, and 42 are also open-centered with the center intersecting through passage 62 such that fluid not used by the first valve in the series flows past the center through passage 62 and is made available for the downstream spool, and so on, for the series. The through passage comprises a series of Y-shaped passages 74, 76, 78, and 80 overlapping at the bores and interconnected thereby.

With the distributor spools in their neutral position, as illustrated in FIG. 2, for example, fluid entering the valve body at inlet 68 will flow across spool 38 into passage 74 where fluid from inlet 70 joins it for continuing flow across spool 40 into passage 76 and across spool 42 into pasage 78, where it then continues across spool 44 and exits from the valve body by way of a drain or return passage 80. With a system as illustrated in FIG. 1, the fluid will flow by way of a conduit 82 to the inlet of the valve assembly comprising distributor valves 26 and 28 to be combined therein with flow from pump 10. Fluid entering the valve body 52 by way of inlet 72 will, in this illustrated embodiment of FIG. 1, be fluid which is supplied from pump and has passed through the open centers of the valve bank in the right hand side of FIG. 1. This fluid has left that valve bank and flowed along a conduit 84 to the inlet 72. With the valve system of FIG. 2 in its neutral position, this fluid entering at inlet 72 will pass along bore 60 and valve stem 44 into a passageway 86 and then to branch 66 of the exhaust passageway and then out exhaust port 88 to be returned to the tank or sump.

Looking now to the valve spool 38, we see that if the spool is moved to the left, such that lands 90 and 92 block the flow of fluid from inlet 68 into the passageway 74, the fluid pressure will open check valve 94 permitting the fluid to flow into branch passage 96. It will then be seen that communication will be established between the branch supply passage 96 and a high pressure motor port 98 by means of a groove 100 formed between lands 92 and 102 on valve spool 38. At the same time, groove 184 formed on spool 38 between lands 106 and 108 will have established communication between another high pressure motor port 110 and branch 64 of the exhaust passageway.

Thus, when high pressure fluid is being supplied to one side of a reversible motor, fluid from the other side of the motor is being exhausted. Similarly, a movement of the spool 38 to the right, will reverse the above fluid flow process and consequently the reversible motor.

Both sides of the motor circuit are protected against excess pressures by means of a high pressure relief valve 112 provided between motor port 110 and exhaust branch 64 and a high pressure relief valve 114 provided between high pressure motor port 98 and exhaust branch 66. Similarly, each side of the motor is protected against cavitation by means of an anticavitation valve 116 between motor ports 110 and exhaust passage 64 and an anti-cavitation valve 118 provided in the passageway between motor port 98 and the exhaust passage 66. These valves operate in the usual manner independently of the valve spool 38. When excess pressures are reached in the motor port 110 the valve 112 will open and relieve pressure into the exhaust passageway 64. Conversely, when pressure in high pressure motor passage 110 drops below that in the low pressure exhaust passageway 64, such as when the motor is over-speeding or over-running, the anticavitation valve 116 will open and permit fluid to pass from the exhaust passageway 64 into the motor passageway 110 to supplement fluid being supplied thereto by means of the pump.

The fluid passageway arrangement for spool 40 is similar to that of spool 38 wherein fluid blocked in the through passage flows past a check valve 119 to branched supply passage 120 wherein communication may then be established with a high pressure motor port 121 or 122 by means of grooves 124 and 126 formed in the spool 40. A pair of high pressure relief valves 128 and 130 are provided between the high pressure motor ports 121 and 122 and the respective branches 66 and 64 of the exhaust passageway. A pair of anti-cavitation valves 132 and 134 are also provided between the motor ports 121 and 122 and the respective branches 66 and 64 of the exhaust passageway.

In the illustrated embodiment, the spool 40 controls the flow of fluid to and from the track motors and for this reason is provided with a pair of retarding or antioverspeed valves 136 and 138 which are operative to retard the flow of exhaust fluid from the motors to prevent the motors from over-running or running away such as to cause loss of control of the vehicle. These valves comprise spools 140 and 142 slidably mounted in bores 144 and 146 and biased by means of springs 148 and 150 to a position to permit communications by way of passages 152 and 154 and grooves 156 and 158 with the exhaust passages 66 and 64. Passages 159 and 160 provide communication between the motor ports 121 and 122 and chambers 161 and 162 at the ends of the spools 140 and 142. If, for example, motor port 121 is being exhausted to exhaust passageways 66 by way of passageway 152 and groove 156 the pressure buildup in port 121 resulting from over-running of the motor such as when the vehicle may be descending a grade,

will be communicated by way of passage I59 to the end of spool 140 and chamber 161 forcing the spool 140 to move to the right and restrict the flow of fluid across the groove 156. When the pressure drops back to a reasonable level, the spring 148 will force the spool 140 back to the left providing full open communication between passageway 152 and passageway 66. Thus it can be seen that the spool 140 operates automatically in response to over-running of a motor connected with passageway 121, and thus provides an automatic retarding on the motor itself. The spool 142 operates in an identical manner to control the flow of fluid through the motor port 122.

From the foregoing description, it can be seen that the spool 38 can operate a suitable motor from a supply of fluid through inlet 68 while at the same time fluid flowing through inlet 70 may be diverted by means of spool 40 for operation of a motor connected to ports 121 and 122 completely independent of the supply fluid through inlet 68. When the control spool 38 is returned to its neutral position, the fluid supplied to inlet 68 then flows into passageway 74 and becomes available together with the fluid through inlet 70 to be directed by means of spool 40 for control of the motors connected to passages 121 and 122. Thus, it can be seen that the first spool 38 is operative to control the flow of fluid from the first inlet opening 68 while at the same time spool 40 may be operative to control the flow of fluid from inlet 70 independent of the inlet 68 and, in addition, is operative to control the combined flow from 'the two inlets 68 and 70.

The control spool or distributor 42 has inlet and control passages arranged similarly to the previous control spools. Movement of spool 42 in either direction blocks the flow of fluid from passage 76 to passage 78 and directs the fluid past check valve 164 into branch passage 166 where it may then be directed by means of grooves 168 and 170 to the motor ports 172 and 174. A pair of high pressure relief valves 176 and 178 provide communication between the motor ports 172 and 174 in case of excess pressure therein to exhaust ports 64 and 66. A pair of anti-cavitation valves 180 and 182 provide communication between the exhaust passageways in the motor ports in the event of a drop of pressure in the motor line which is likely to cause cavitation.

A cross-over spool 44 which is operatively coupled to move with the control spool 42 and facilitate combining of fluid from inlet 72 with that from passageway 76 for distribution by means of spool 42 to a suitable motor connected with motor passages 172 and 174. Thus, movement of spool 42 causes spool 44 to move in the same direction, thus blocking flow of fluid from the inlet 72 to passageway 86 causing it to open check valve I84 and permit flow into passageway 166 where it combines with fluid from passageway 76 for operation of motors controlled by the stem 42. Thus, it is apparent that the spool 42 in conjunction with the spool 44 is operative to combine a flow of fluid from the first inlet 68, second inlet 70, and a third inlet 72 for operation of a selected motor. Also, the valve stems 42 and 44 are capable of supplying fluid from a source 72 for operation of motor at the same time that valves 40 and 38 are being operated for control of. their respective motors. In other words, the motor operated by valve stem 42 may be operated from a number of sources of fluid either independently or combined. Thus, the unique valve arrangement and cooperating relationship of the valve assembly of the present invention is capable of providing for extremely versatile operation of a plurality of hydraulic implements such as a backhoe or hydraulic excavator.

The embodiment showing FIG. 3 is identical to that of FIG. 2, with the exception that the stems 42 and 44 of FIG. 2 have been replaced by stems 188 and 190 with the stem 188 having a completely open center and the through passage blocking function performed by means of the central land 192 rather than by land on valve 42 as shown in FIG. 2. This arrangement has the advantage of distributing the functions of spools such that the crossover spool 190 performs more of the function than in the previous embodiment.

FIG. 4 is a sectional view through an actual valve body and illustrates, among other things, that each of the valve elements or distributor spools are held in place by compression spring arrangement. Spool 38, for example, has a compression spring 193, positioned between washers 194 and 196 which are slidably mounted on the spool 38 and bear against shoulders thereon for maintaining the spool in the central posi' tion. The washer 196 biases against a cap member 198 to maintain it in its fixed position with respect to housing 52. The spool or distributor 40 is similarly provided with a similar spring 200 for maintaining it in the neutral position. In addition, provided at each end of the spool 40 are chambers 202 and 204 into which fluid is introduced by means of conduits 206 and 208 for pilot operation of the valve. The spools I88 and 190 are coupled together by a coupling member 210 for movement together and are provided with suitable centering means such as springs 212 and 214 arranged as described above. Another feature of interest as shown in FIG. 4 is that the outlet from spool 38 and the inlet to spool 40 are actually coupled together in the actual embodiment by means of an external conduit 216 although the passageway could conveniently be placed within the valve body itself. This arrangement permits a complete separation of the circuit controlled by distributor spool 38, and of distributor spool 40.

An additional feature of the valve assembly, illustrated in FIG. 5, is a further inlet opening 218 which may be provided for directing fluid to the spool 188. Thus an additional source of fluid may be provided such that fluid is always available to the valve 188 despite upstream operation by the other valves.

FIG. 6 illustrates the actual construction arrangement at cross-over valve 190 and the relationship of the inlet 72 and outlet 80.

FIG. 7 illustrates an alternate embodiment having two cross-over or combining spools. One spool provides for combining a new source of fluid with the supply at the control spool. The other spool provides for diverting fluid downstream of that spool to provide a source to be used by another spool.

In particular, there is disclosed in FIG. 7, a valve system comprising a housing 220 having a plurality of control spools 222, 224, and 226 constructed and arranged substantially as disclosed in the previous embodiments. The porting and passage arrangement, however, is such that three different supplies are available selectively, individually or combined at certain control spools. For example, an inlet 228 supplies fluid from a first pump or source solely to control spool 222, where it is either used or returned via outlet 230 to reservoir.

A second inlet 232 supplies fluid from a second pump or source to control spool 224. This fluid, if not used, passes along through passage 234 and becomes available to be used by control spool 226. The fluid continues past spool 226 if not used there, along passage 236 where it crosses a combining spool 238 and into a return or exhaust passage 240 for return to reservoir. The spool 238 is operative upon movement to the right to block the flow of fluid to exhaust 240 and cause it to flow past a check valve 242 to an outlet passage 244 to become available to another circuit. Thus, in the arrangement as illustrated in FIG. 1, the fluid from one bank of valves would become selectively available to the other bank when not used in the first.

A third inlet 246 supplies fluid to a combining or cross-over spool 248 disposed in a bore 250. The fluid is permitted to flow along the spool and out to exhaust passage 240 when the spool 248 is in neutral. Upon actuation of spool 248, the fluid is forced to flow along passage 252 through check valve 254 to combine at spool 226 with fluid from passage 234. The valve 248 may be coupled to spool 226 either mechanically or hydraulically to move therewith for automatic combining when fluid is available. Alternately, the spool 248 may be independently operable for selective combining when fluid is available at inlet 246.

The selective combining feature is important in situations such as in operation of a hydraulic excavator wherein at one minute the operator is carrying out rapid excavation and at the next minute he may be trimming the excavation at a point adjacent underground utility lines or the like. In the second instance, it is necessary that he have full and precise control of the movement of the tool. Such precise control is best achieved with lower volume of fluid modulated by the main control spool.

From the above description it is seen that there is disclosed various control valve arrangements having a plurality of main control spools, and means operative to combine fluid from a plurality of sources at selected main control spools.

While the present invention has been described with respect to specific embodiments, it is apparent that numerous changes and modifications may be made in the disclosed structure without departing from the spirit and scope of the present invention as defined in the appended claims.

We claim:

I. A control valve, said valve comprising:

a housing having a cylindrical bore formed therein;

a first inlet passageway communicating with the center of said bore;

an outlet passageway communicating with said bore adjacent the communication of said inlet passage and communicating along said bore with said first inlet passageway;

a pair of motor control passages communicating with said bore;

a pair of exhaust passages communicating with said bore;

an open-centered first control spool disposed in said bore and operative to control the flow of fluid between said passageways;

a second bore disposed parallel to said first bore;

said through passageway communicating with said second bore;

a second inlet passageway communicating with said second bore and with a second through passage normally communicating with said exhaust passage;

a combining passageway for providing communication between said second inlet passage and said first inlet;

a second control spool disposed in said second bore and operative to direct fluid from said second inlet to combine with fluid from said first inlet for control by said first spool; and,

said first and second spools are operatively coupled together.

2. The invention of claim 1 wherein said coupling is hydraulic.

3. A control valve, said valve comprising:

a housing having a cylindrical bore formed therein;

a first inlet passageway communicating with the center of said bore;

an outlet passageway communicating with said bore adjacent the communication of said inlet passage and communicating along said bore with said first inlet passageway;

a pair of motor control passages communicating with said bore;

a pair of exhaust passages communicating with said bore;

an open-centered first control spool disposed in said bore and operative to control the flow of fluid between said passageways;

a second bore disposed parallel to said first bore;

said through passageway communicating with said second bore;

a second inlet passageway communicating with said second bore and with a second through passage normally communicating with said exhaust passage;

a combining passageway for providing communication between said second inlet passage and said first inlet; and,

a second control spool disposed in said second bore and operative to direct fluid from said second inlet to combine with fluid from said first inlet for control by said first spool;

a third control spool co-axially mounted with said mounted spool in said second bore; and,

said third spool being operative to divert fluid from said through passage downstream of said first control spool for use by another control spool.

4. The invention of claim 3 wherein said second spool is operative with said first spool and said third spool is operative with said other spool.

5. A hydraulic valve assembly for controlling bidirectional motion of a plurality of fluid motors, said valve assembly comprising:

a valve body having a plurality of parallel bores;

a plurality of valve elements slidably mounted in said bores;

a pair of said valve elements operatively coupled to move together;

a first stem mounted for movement in a first bore;

an intake passageway connectable with a first source of pressurized fluid and communicating with said first bore for admitting pressurized fluid thereto;

an intake connectable with a second source of pressurized fluid and communicating with a passageway between said first bore and a second bore; and,

said pair of valve elements being responsive to combine the fluid from said inputs and direct it to a selected one of said outputs.

6. A bank of control valves comprising a housing having a plurality of parallel bores and a slidable spool in each of said bores;

a plurality of inlet openings;

a common exhaust passage intersecting all of said bores;

a through passage intersecting all of said bores;

a pair of high pressure motor ports intersecting each of said bores;

a first slidable spool operative to control the flow of fluid from a first inlet opening;

a second slidable spool operative to control fluid from a second inlet and from said first inlet; and.

a third slidable spool operative to control fluid from a third inlet and from said first and second inlets.

7. The invention of claim 6 comprising a fourth spool operatively connected to operate with said third spool.

8. The system of claim 6 wherein each of said bores are intersected by a pair of high pressure motor ports and a branched exhaust passage.

9. The system of claim 8 comprising a pair of anticavitations and relief valves controlling a passageway between each of said high pressure motor ports and a branch of said exhaust passage. 

1. A control valve, said valve comprising: a housing having a cylindrical bore formed therein; a first inlet passageway communicating with the center of said bore; an ouTlet passageway communicating with said bore adjacent the communication of said inlet passage and communicating along said bore with said first inlet passageway; a pair of motor control passages communicating with said bore; a pair of exhaust passages communicating with said bore; an open-centered first control spool disposed in said bore and operative to control the flow of fluid between said passageways; a second bore disposed parallel to said first bore; said through passageway communicating with said second bore; a second inlet passageway communicating with said second bore and with a second through passage normally communicating with said exhaust passage; a combining passageway for providing communication between said second inlet passage and said first inlet; a second control spool disposed in said second bore and operative to direct fluid from said second inlet to combine with fluid from said first inlet for control by said first spool; and, said first and second spools are operatively coupled together.
 2. The invention of claim 1 wherein said coupling is hydraulic.
 3. A control valve, said valve comprising: a housing having a cylindrical bore formed therein; a first inlet passageway communicating with the center of said bore; an outlet passageway communicating with said bore adjacent the communication of said inlet passage and communicating along said bore with said first inlet passageway; a pair of motor control passages communicating with said bore; a pair of exhaust passages communicating with said bore; an open-centered first control spool disposed in said bore and operative to control the flow of fluid between said passageways; a second bore disposed parallel to said first bore; said through passageway communicating with said second bore; a second inlet passageway communicating with said second bore and with a second through passage normally communicating with said exhaust passage; a combining passageway for providing communication between said second inlet passage and said first inlet; and, a second control spool disposed in said second bore and operative to direct fluid from said second inlet to combine with fluid from said first inlet for control by said first spool; a third control spool co-axially mounted with said mounted spool in said second bore; and, said third spool being operative to divert fluid from said through passage downstream of said first control spool for use by another control spool.
 4. The invention of claim 3 wherein said second spool is operative with said first spool and said third spool is operative with said other spool.
 5. A hydraulic valve assembly for controlling bi-directional motion of a plurality of fluid motors, said valve assembly comprising: a valve body having a plurality of parallel bores; a plurality of valve elements slidably mounted in said bores; a pair of said valve elements operatively coupled to move together; a first stem mounted for movement in a first bore; an intake passageway connectable with a first source of pressurized fluid and communicating with said first bore for admitting pressurized fluid thereto; an intake connectable with a second source of pressurized fluid and communicating with a passageway between said first bore and a second bore; and, said pair of valve elements being responsive to combine the fluid from said inputs and direct it to a selected one of said outputs.
 6. A bank of control valves comprising a housing having a plurality of parallel bores and a slidable spool in each of said bores; a plurality of inlet openings; a common exhaust passage intersecting all of said bores; a through passage intersecting all of said bores; a pair of high pressure motor ports intersecting each of said bores; a first slidable spool operative to control the flow of fluid from a first inlet opening; a second slidable spool opeRative to control fluid from a second inlet and from said first inlet; and, a third slidable spool operative to control fluid from a third inlet and from said first and second inlets.
 7. The invention of claim 6 comprising a fourth spool operatively connected to operate with said third spool.
 8. The system of claim 6 wherein each of said bores are intersected by a pair of high pressure motor ports and a branched exhaust passage.
 9. The system of claim 8 comprising a pair of anti-cavitations and relief valves controlling a passageway between each of said high pressure motor ports and a branch of said exhaust passage. 